This work describes the design methodology and development of piezoelectric transducers for applications in fluids with COMSOL_Multiphysics. In these linear models for the acoustic-structure interaction approximate numerical solutions have been obtained. In order to perform the calculations, simplifications are only valid for low-power sound waves. Numerical modeling of piezoelectric transducers implies coupling the physics associated with piezoelectric elements, structural elements and fluid elements, resulting in complex models with difficult convergence. The selection of appropriate mesh refinement, boundary conditions and configuration parameters of the calculation methods is of great importance to obtain the numerical result. The use of high-intensity ultrasound to improve mass transfer efficiency in fluids under supercritical conditions, is presently a novel technique for the extraction of natural products.